1. Technical Field of the Invention
The present invention relates generally to brush assemblies and alternators. More particularly, the invention relates to a brush assembly for use in an alternator, which can be easily installed to the alternator and can reliably prevent foreign matters from entering the inside thereof during operation of the alternator.
2. Description of the Related Art
In automotive alternators, it is required to prevent foreign matters, such as water and oil, from invading sliding contact portions between brushes and slip rings, thereby preventing abnormal abrasion of the brushes.
Moreover, in automotive alternators, it is also required to exhaust brush powders produced by sliding contacts between the brushes and the slip rings and to suppress temperature rises of the sliding contact portions due to frictional heat generated by the sliding contacts.
To meet the above requirements, Japanese Patent First Publication No. 2002-359951 discloses a brush assembly employed in an automotive alternator, which has a structure designed to introduce cooling air to the vicinity of the sliding contact portions between the brushes and the slip rings. The brush assembly includes a brush holder holding the brushes therein and a slip ring cover configured to cover the slip rings. The installation of the brush assembly to the alternator is performed with the brush holder and the slip ring cover assembled together.
More specifically, the brush holder includes therein springs configured to respectively press the brushes against the slip rings. To prevent the brushes pressed by the springs from interfering with the slip rings during the installation of the brush assembly onto a rotary shaft of the alternator, the brush holder and the slip ring cover are configured to respectively have first and second through-holes. In the installation, the brush holder and the slip ring cover are first assembled together, thereby bringing the first and second through-holes into alignment with each other. Then, a rod-like retainer is placed through both the first and second through-holes, thereby retaining the brushes in the brush holder against the spring forces of the springs. After that, with the brushes retained in the brush holder by the retainer, the brush assembly is installed to the rotary shaft of the alternator without causing interference between the brushes and the slip rings. After the installation, the retainer is removed from the brush assembly, leaving the first and second through-holes in alignment.
With the above configuration, it is easy to install the brush assembly onto the rotary shaft of the alternator.
However, during operation of the alternator, foreign matters may enter the inside of the brush assembly through the first and second through-holes that are in alignment, thus causing abnormal abrasion of the brushes.